Caption: Clostridium difficile bacteria, coloured transmission electron micrograph (TEM). This bacterium is a normal inhabitant of the human gut, and is resistant to most antibiotics. It normally causes no problems, but if a patient is given a course of broad-spectrum antibiotics for another infection, that may kill all the other bacteria in the gut, leaving just C. difficile. In this case it flourishes, and can cause pseudomembranous colitis, a potentially fatal inflammation of the colon. C. difficile can form spores (pale ovals) to survive harsh conditions, and can survive for weeks in hospitals on surfaces. Magnification: x9000 when printed 10cm wide.